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Expert: Another ‘Big One’ is possible

From the print edition

The trembling continues. 

After a magnitude-7.6 earthquake shook Costa Rica on Sept. 5, the country has registered some 1,800 aftershocks. The quake did minimal damage – mainly battering buildings and highways in the provinces of Guanacaste and Alajuela – in spite of its remarkable magnitude.

But residents remain on edge both due to the aftershocks and predictions of another major earthquake. 

On the Nicoya Peninsula, near the earthquake’s epicenter in Sámara, Guanacaste, the shakes come frequently. No injuries and only superficial damage have been reported from the aftershocks. Still, locals describe only brief intervals of relief from the trembling earth, which rattles buildings and those inside them – little reminders of the “big one” that hit Nicoya a week earlier.

“It’s been crazy with all the aftershocks,” said Kristina Hughes, 27, who lives in the Pacific coastal town of Tamarindo. “I work from home and feel [aftershocks] all day. The one on Monday night at 8:15 was so strong we ran outside. My boyfriend and I even moved our bed into the living room near the front door and packed an emergency kit. I don’t think we’ll have to use it, but I just hope they stop sooner rather than later.”

The strongest aftershock was felt last Saturday, with a magnitude of 5.6. Costa Rican seismologists said the aftershocks would persist throughout the week. The magnitudes and frequencies of the tremors should decrease, they said, ranging from 2 to 3 in magnitude. 

The Volcanological and Seismological Observatory of Costa Rica (Ovsicori) released its conclusions in regards to the quake Tuesday. The organization confirmed that this was the “big one” – the powerful earthquake long expected in Nicoya. However, the news came with another caveat. 

The fault did not rupture all of its energy. The earthquake only released 40 percent of the pent-up energy at the fault line. Marino Protti, Ovsicori’s lead scientist who has predicted a major earthquake would occur in the area for more than a decade, summarized that the rest of the energy could be released in several ways, including through another huge earthquake.

“Another earthquake of equal or greater magnitude to what occurred on Sept. 5, is a scenario we cannot dismiss,” Protti said. 

He said predicting when and if another major earthquake could strike is nearly impossible. The release could come in weeks or in decades. The last major earthquake to hit Nicoya – registering magnitude-7.3 – came in 1950. 

Lepolt Linkimer, a seismologist for Costa Rica’s National Seismological Network at the University of Costa Rica, disagreed with the Ovsicori’s statement, telling the daily La Nación the prediction is creating “huge anxiety.”

“What we think is that it is not appropriate to pinpoint a geographic area in Costa Rica, when all of Costa Rica is a risk area [for an earthquake],” Linkimer said.

Throughout the week, Costa Rica began to return to normalcy, after enduring one of the strongest earthquakes in the country’s history.

On Monday, students in Guanacaste went back to school, after the tremors cancelled classes last week. Classes were back in session at 41 schools. 

Yet students and teachers didn’t all return to classrooms. Some classes were held in local churches, cafeterias and community centers, according to the daily La Nación, as some schools suffered severe damage.

The National Emergency Commission began to finalize damage statistics this week, Radio Reloj reported. The commission, while working with the Housing Ministry, reported 494 homes were damaged. Sixty of those homes qualified as having “severe damage,” with more than half located in Nicoya. 

The total cost of insured losses from the quake should not exceed $100 million, according to catastrophe consulting from EQECAT, Inc. 

Some four dozen people remain in shelters as of Wednesday afternoon. Approximately 30 people were wounded in the quake. Only one death was reported, a 51-year-old Guanacaste woman who died of a heart attack. 

The Education Ministry estimated $6 million is needed to fix the damaged schools. Some media have inquired as to whether the Costa Rican government could use an $8 million gift received from China last month to fund those repairs. Chinchilla said that option remains a possibility.

Insurance companies in the country received more than 2,200 claims for damages, according to La Nación. Inspectors will visit affected areas over the next two weeks to evaluate the claims.

Linkimer told The Tico Times last week the small amount of damage demonstrated the country’s impressive adherence to seismic codes. 

 The lack of severe damage ought to provide some comfort in light of the Ovsicori forecasts calling for another major Nicoya quake during the current seismic cycle. 

Protti added the remaining energy would not necessarily be freed through a strong earthquake. Energy also can be expelled through a “slow earthquake” (a type of weak temblor that releases energy over a period of hours or months instead of seconds). 

Or the release of energy could come through numerous aftershocks. 

“We cannot exactly know how or when it will release the rest of the energy,” Protti said.

Suzanna Lourie contributed reporting from Tamarindo, Guanacaste.

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